current value of inventory in sets

I've noticed this in the past, but it is happening more frequently now. When I look at my inventory tab the value is changing a couple of times a week. I check inventory with a price change but there is nothing listed. Now that I've noticed these changes, I am checking more often. Thankfully it is going up, but I don't know what is driving this if nothing is showing up in my inventory with a price change. Any thoughts?